AYCI: Do NOT use your notes. This fish picture is an example of codominance. IN YOUR OWN WORDS, write an explanation of codominance based on what you have learned so far. RR x WW are parents. Based on the above picture, do you think that the flowers represent codominance as well? Be prepared to explain your answer.
After I check your answers, erase your white boards, put them in your bucket, and return them to the side of the room. AYCI: Using the white boards in your team bucket, on the side of the room, write the answer to the following questions. Get out your sticker sheet before I check your work. 1. In snapdragons, heterozygous flowers are pink, while homozygous flowers are either red or white. When two pink flowers are crossed, what fraction of the offspring will be pink? Create a punnett square to answer the question. A) ¼ or 25% B) ½ or 50% C) ¾ or 75% D) All of them 2. What type of genetic inheritance is described in the above question?
1. B) ½ or 50% R W R RR RW W RW WW 2. Incomplete dominance: this is where two alleles that are both dominant, do not shadow each other, but create a phenotype that is blended between the two parent alleles.
Incomplete Dominance, Codominance, Multiple Alleles, and Sex-Linked Genes
Fill in the blank notes pg. 1 dominant heterozygous Incomplete blending alleles rr RR pink partial
Fill in the blank notes pg. 2 independent roan BB White dominant black both Bb
Fill in the blank notes pg. 3 co-dominant I B I B 3 blood allele i I A i phenotype ii
Exit Slip: Use scratch paper in the green bucket. Turn this into the tray before you leave. Write in complete sentences. Compare and Contrast codominance with incomplete dominance.
Incomplete dominance This is when neither allele is dominant. Both alleles are expressed and contribute equally to the phenotype. A heterozygous genotype has an intermediate phenotype as there is partial influence from both alleles. Example: Red + White = Pink flower flower flower
Incomplete dominance Snapdragons can be red (alleles = RR) white (alleles = rr) pink (alleles = Rr) If you cross two pink flowers, is it possible to produce a white flower? ¼ Red ¼ White ½ Pink Yes!
Codominance Both alleles are dominant. They are independent, so there is no 'blending' as in the snapdragons, instead the phenotype is a result of the full expression of both alleles. Example: black + White = B&W spotted dog dog dog
Codominance Dogs can be Black (alleles = BB) White (alleles = bb) Spotted (alleles = Bb) Is it possible for a black dog to have one parent that is white? No!
Multiple alleles (blood typing) In the case of the ABO blood grouping, there are 3 alleles for one gene They are written a little differently: i : this allele is recessive I A : this allele is co-dominant I B : this allele is co-dominant
Multiple alleles (blood typing) Blood group (phenotype): A.. B.. AB O.. Possible genotype: I A I A or I A i I B I B or I B i I A I B ii
Multiple alleles (blood typing) A father with homozygous type A blood has a child with a mother that has heterozygous type B blood. Is it possible for them to have a child with type O blood?
Sex determination Gender is determined by sex chromosomes in many animals. The XY System: Female are XX, males are XY Y makes the guy!!! What are the odds that a couple have a boy? 50/50
Sex-linked genes Some genes are linked to the sex chromosomes and are inherited with them. Hemophilia is carried on the X chromosome. The normal allele is dominant (H) The allele for hemophilia is recessive (h)
Sex-linked genes X H X H = normal female X H X h = carrier female X h X h = female w/hemophilia X H Y = normal male X h Y = male w/hemophilia A carrier does not have the disease, but can pass it on to their offspring.
Sex-linked genes If a female carrier has offspring with a normal male, what is the chances that their offspring will have hemophilia? 25%
Sex-linked genes In cats the allele for coat color is carried on the X chromosome. The alleles are black and orange but they are codominant. X B X B = black female X B Y = black male X b X b = orange female X b Y = orange male X B X b = tortoiseshell female
Sex-linked genes Can an orange male and a black female produce a tortoiseshell male? No!
What is the genotype of the father? Sex-linked genes
Sex-linked genes Mother can provide X B or X O Father can provide Y plus 1 other allele. Since 1 offspring is X O X O, the father must provide 1 of these allele. Therefore, the father's genotype is X O Y